Casting easily oxidizable metals



Patented July 19, 1932 UNITED STATES PATENT OFFICE ROBERT THOMAS WOOD, OF LAKEWOOD, OHIO, ASSIGNOR, BY MESNE ASSIGNMENTS, TO

MAGNESIUM DEVELOPMENT CORPORATION, A CORPORATION OF DELAWARE CASTING EASILY OXIDIZABLE METALS No Drawing.

This invention relates to the casting of the easily oxidizable metals in molds made of sand or similar agglomerated materials. The invention is particularly directed toward processes and means by which the casting of these metals may be accomplished without the attendant well known difficulties heretofore encountered. Of the easily oxidizable metals magnesium is commercially the most important.

The propensity of metals of the class mentloned to react violently with moisture and to combine with the oxygen and nitro en of the atmosphere has been .a serious 0 stacle to their successful casting in sand molds. In accepted foundry practice for ordinary metals there 1s usually added to the sand or other similar molding materials a tempering medium, 1n most cases water, which imparts to the sand the properties necessary to satisfactory moldlng. It was accordingly supposed that 1n order to successfully cast magnesium and similar metals in such molds, the mold must be drled by careful heating in order to prevent attack of moisture on the molten metal.

To overcome the well known difiiculties, several methods have been suggested. For example, it has been proposed, in conjunctlonwith the drying method, to incorporate 1n the molding material a substance which, when the mold becomes heated, will produce a vapor around the metal to protect it from the atmosphere. Obviously the vapor of such a protective substance must have little or no effect on the metal. It has also been proposed to use certain protective substances such as sulfur, urea, oxalates, or boric acid, which are reported to be usable in an undrled sand mold, in the belief that the vapors given ofl by these substances, when heated, would adequately isolate the metal and protect the same from attack by moisture in the mold. Practice, however, has shown that of these substances sulfur alone exerts a protective action sufiicient to permit the use of water as a Application filed October 23, 1929. Serial No. 401,959.

tempering medium if good castings of commercial size are to be produced.

In spite of the numerous investigations which have been undertaken relative to the casting of the easily oxidizable metals in sand molds, the commercial foundry is still faced with difliculties when casting these metals. The drying of the mold is a tedious, expensive process and the incorporation of a protective substance has not been found to produce in all instances the desired effect. As stated above, sulfur may be employed to eliminate the necessity of drying the mold; but in this case also, the castings produced do not represent the optimum in desirable characteristics.

The chief object of the present invention is to provide an improved method of utilizing the protective idea with easily oxidizable metals, to enable sound castings to be obtained, in a commercial foundry, of a good color and free, or substantially so, from oxld films and blow holes. Further objects are to provide a method for the production of sounder and cleaner castings of large size than has heretofore been considered possible; to provide new protective substances and molding mixtures containing the same, by which these methods may be carried out; and to modify and adapt, some of the previously known protective substances so as to roduce a more eflicient protective effect, partlcularly in molds containing moisture.

My invention is developed-from and predicated upon an investigation extending over a considerable period of time. In the course of this investigation, in which new and also previously known protective substances were used in both dried and undried sand molds and easily oxidizable metals, notably magnesium and its alloys, were cast therein under varied commercial foundry conditions,

I observed that while in the presenceof someprotective substances excellent castings might be made there was a tendency for the cast- I have, moreover, found that this method produces better results with smaller castings than had heretofore, within my knowledge, been obtained. My new method,'-briefly stated, comprises, incorporating ammonium bisulfate in the sand or other molding materials to provide a protective vapor around the casting as the mold is heated by the molten metal.

' The invention also includes the use of one or more other substances, capable of producing a metal-protecting vapor at successively higher temperatures, preferably such as to produce collectively a substantially continuous emission of protective vapors as the temperature of the mold rises, thus making possible the presence, in the mold and around the casting, of an adequately protective vapor, regardless of the temperature to which the mold is brought by the hot metal.

casting magnesium or similar metals in sand or the like required thatthe protective substances be incorporated in the sand and that the mold made from this mixture be thoroughly dried before use in order to eliminate whatever water was added to or was present in the sand. Of the protective substances suggested for use in such dried molds, the polyhydric alcohols and specifically glycerin had been found to be especially eificacious. It had been thought however, that such polyhydric alcohols were eflicient only when used in dried sand molds. I have found that the contrary is true and that when combined with other protective substances, for example sulfur, ammonium bisulfate, ammonium fluorid, naphthalene, and especially boric acid, these alcohols may be used in a moist sand mold with good results. This leads to important advantages, for in the older methods of using the polyhydric'alcohols the sand was dried before molding and enough of such alcohols was then added not only to protect the metal but also to lendthe proper mold;- mg qualities to the sand. By the use of the polyhydric alcohols in aqueous solutions according to my invention, the drying of the sand is rendered unnecessary and the sand is found to have improved molding qualities as compared to ones using a non-aqueous solution of polyhydric alcohol as the tempering medium. Moreover, the amount of the alcohol required is materially reduced since it is no longer necessary to add more alcohol than will produce the desired protective effect on the metal. Although glycerin has been mentioned as the desirable polyhydric @1 69- hol for use as a protective substance, I have found that when used in. aqueous solutions ethylene glycol and di-ethylene glycol are markedly superiorto glycerin in that substantially the same effect is produced by the use of a 25 per cent aqueous solution of either ethylene or di-ethylene glycol as can be produced by the use of a per cent solution of glycerin.

In using aqueous solutions of one of the polyhydric alcohols, such as glycerin, ethyl-v ene glycol, or di-ethylene glycol, it was noted that withboric acid also present, results were produced which were superior to those obtained with molds lacking this particular combination of protective substances. As a result of my investigations I believe this unexpected effect is caused by' the presence, in the sand, of what is probably an'organic borate, formed by reaction between the poly hydric alcohol and the boric acid at the elevated temperatures to which the mold is brought by the molten metal. Beilsteins Handbook of Organic Chemistry lists a compound having the formula (C3H5O5B) x which, it is stated, may be obtained by heating glycerin and boric anhydrid together. Most of the methods heretofore devised for My experimentsindicate thatwhen glycerin and boricacid are present in the sand the compound by Beilstein, or one-much like it, is formed as the mold becomes heated. Possibly the compound produced when ethylene glycol is used has the analogous formula H O B) Whatever the actual composition may be, I use the expression organic borate hereinafter to include the compound just referred to and similar compounds, as for example the one listed in Beilstein above and the one formed by reaction between boric acid and di-ethylene glycol. At any rate, by adding to the molding sand 9. compound formed by the reaction between boric acid and ethylene or (ii-ethylene glycol, which is presumably an ethylene borate, or, more generally, an organic borate, I have achieved practically the same results as those obtained with a mixture of boric acid and a polyhydric alcohol. The use of an organic borate alone, or of boric acid and a polyhydric alcohol without other protective substance, ives a protective effect on magnesium or li e metals which is superior to that obtained with any one sub stance heretofore known to me, and the castings produced are in quality second only to those obtained in molds containing a plurality'of protective substances of variant vaporizing temperatures. In using boric acid and a polyhydric alcohol (with consequent formation of an organic borate when the metal is poured), I have found that excellent commercial results can be obtained by incorporating in the molding sand 1 to 3 per cent (by weight) of boric acid and then adding to the mixture enough of a 25 to 75 per cent (preferably about 40 per cent) aqueous solution of ethylene or di-ethylene glycol to give the desired molding qualities. In molds formed of such sand I have produced mag- V nesium and magnesium alloy castings of dis- 5 tinctly superior quality, both from the standpoint of soundness and strength and from the standpoint of color. Other quantities of boric acid and other amounts of the same or another polyhydric alcohol may be mixed with the sand and very good results obtained. I have also found that as a substitute for boric acid ammonium borate may be employed; or borax and a mineral acid, say hydrochloric or sulfuric, which will react with the borax to produce boric acid. These substitutes will give, in combination with the polyhydric alcohol, substantially the same results as are obtained with boric acid and the same alcohol.

In the further course of my investigations I have found other substances, namely potassium sulfid and ammonium bisulfate, which when incorporated in the sand and heated by the molten metal, also exert a protective action sufficientto make possible the production of good castings of the readily oxidizable metals, and they have, moreover, a protective action even in undried molds. These substances, potassium sulfid and ammonium bisulfate, may be used singly; or either may be used with other protective substances in the same mold. Each ofthem, when present as the only added protective substance, say to the amount of about 2 per cent of the total solids of the mixture, will make possible the production of castings of limited size in undried sand molds. As between them, ammonium bisulfate is in' general preferred. Moreover, either or both of these two substances, the protective properties of which were heretofore unknown, may be used advantageously in practicing my described method of producing large sized castings by means of a plurality of protective agents.

Other substances, some of them already known, may also be used in the above mentioned method. Among these are sulfur, ammonium fluorid, urea, magnesium oxalate.

:0 magnesium fluoride, ammonium chlorid, and

naphthalene. Many of these substances used singly as the protective substance in dried d sand molds do not exert a very efficient protective effect, and only certain of them have 5 heretofore been supposed capable of exerting a protective actionjin the presence of moisture. For instance it has been believed heretofore that naphthalene is a successful protective substance only when it is mixed with 0 dried sand, and in one instance at least the use of this compound, in combination with a resin, has been suggested to overcome the diificulties incident to molding when no water is used as binder. I have found, however, 5 that naphthalene in amounts of 7 to 10 per cent by weight of the total mixture, exerts a protective effect in moist sand which is in some cases adequate, especially for magnesium. I have also discovered that similar hydrocarbons, suchas anthracene, chrysene, etc., produce similar results and I consider them to be substantial equivalents of naphthalcne. All of the above mentioned protective substances I have used in carrying out my novel method above described. Some are better than others but all, when used With other substances in accordance with my method, produce an effect superior to that I produced by any one of them singly.

glycerin 290, sulfur 440, ammonium bisul-' fate 490. Boric acid volatilizes in steam and in polyhydric alcohols. Ammonium fluorid has no true boiling point but it begins to vaporize and dissociate at comparatively low temperatures. Of ethylene borate it can be said that when the compound is produced by heating ethylene glycol and boric acid in water to simulate the conditions occurring in a sand mold distillates are obtained from about 120 C. to as high as 280 which upon analysis are found to contain boron and organic matter. This is probably one reason why ethylene glycol and boric acid are so effective when used together. In some cases I prefer to use an organic borate, for example, the ethylene borate just mentioned, as at least one of the plurality of protective substances, and sulfur as another, since I have found that molding mixtures containing the substances named are capable of producing better and larger castings than could heretofore be obtained. However, the presence of both these particular substances is not necessary to prouce large sized castings or to produce smaller sized castings of a quality not heretofore obtainable, and in fact in some cases a combination containing only protective substances which were Well known before my present invention, produces results superior to any which .were heretofore obtained. Among substances usable alone, organic borate, sulfur, naphthalene, and ammonium bisulfate are especially effective, and one or more of these substances are included in each of the mixtures outlined below, but the invention is by no means limited in that respect. Instead of preparing in advance the organic borate which is formed (I believe) by reaction of the boric acid and ethylene or diethylene glycol, for example, it is in general more advantageous to produce the same in situ, so to speak, by incorporating the necessary reagents in the molding mixture. I may 7 also use to advantage ammonium phosphate,

the use of which is more fully described in the copending application of Francis C. Frary and myself, Serial No. 401,962, filed concurrently herewith.

In the following examples and in the appended claims the term sand is intended to include not only that particular material but similar inactive materials which, in commonly accepted molding practice, are used to form molds of the agglomerated or non-permanent type. These examples (in which the parts stated are by weight) represent a number of molding compositions which have been found especially advantageous in casting the easily oxidizable metals and particularly magnesium and its alloys, according to the precepts of my invention. The water or other tempering medium is added in amount sufiicient to give the desired molding consistency.

Example 1 Molding sand approximately 88 parts Sulfur do 6 parts Naphthalene do 4 parts Ammonium bisulfate do 2 parts Water Suflicient Example 2 Molding sand approximately 93 parts Naphthalene do 4 parts Ammonium bisulfate do 2 parts Boric aci do 1 part Ethylene glycol, 60 per cent aqueous solution Suflicient Ewample Molding sand approximately 90 to 88 parts Organic borate do 3 to 5 parts Sulfur-n do 2 to 2 parts Naphthalene do 3 to 3 parts Ammoni bisulfate do 2 to 2 parts Water Sufiicient 'filed of even date herewith.

I claim 1.-The method of casting magnesium and other easily oxidizable metals in sand molds, comprising with sand a plurality of metals in sand molds, comprising mixmg with sand 2. pluralityof protective substances of variant vaporizing temperatures, including ammonium bisulfate, and boric acid and an aqueous solution of di-ethylene glycol; forming a mold of the mixture; and casting the metal in the mold.

3. The method of casting easily oxidizable metals in sand molds, comprising mixing with sand a plurality of protective substances of variant vaporizing temperatures, including ammonium bisulfate, sulfur, naphthalene, and boric acid and a solution of die'thylene glycol; making a mold of the mix ture; and castin the metal in the mold.

4. The metho of casting magnesium and other easily oxidizable metals in sand molds, comprising mixing ammonium bisulfate, sulfur, boric acid and a solution of di-ethlyene glycol, and sand; forming a mold of the mix ture; and casting the metal in the mold.

5. The method of casting magnesium and other easily oxidizable metals in sand molds, comprising mixing with sand ammonium bisulfate, sulfur, boric acid and a solution of a polyhydric alcohol; making a mold of the mixture; and casting the metal in the mold.

6. The method of casting magnesium and other easily oxidizable metals in sand molds,

comprising casting the ammonium bisulfate and sulfur, and material adapted to give oif a vapor of an organic borate, and producing thereby around the metal in the mold a plurality of protective vapors including a vapor of an organic borate. I

7 The method of casting magnesium and other easily oxidizable metals in sand molds, comprising casting the metal in a mold formed of sand containing ammonium bisulfate and material adapted to give off a vapor of an organic borate, and producing thereby around the metal in the mold a plurality of protective vapors including a vaporof an organic borate.

8. Themethod of casting magnesium and other easily oxidizable metals in sand molds, comprising mixing sand and a plurality of protective substances of variant vaporizing temperatures, including ammonium bisulfate, forming a mold of the mixture, and casting the metal in the mold.

9. The method of casting easily oxidizable metals in sand molds, comprising mixing with the sand about 2 per cent of ammonium bisulfate, forming a mold of the mixture, and casting the metal in the mold.

10. The method of casting magnesium and.

metal in a mold made. of sand containing in admixture therewithother easily oxidizable metals in sand molds, comprising mixing ammonium bisulfate with the sand, forming a mold of the mixture, and casting the metal in the mold.

11. The method of casting magnesium and other easily oxidizable metals in sand molds,-

nature.

ROBERT THOMAS WOOD. 

